Airfoil construction



April 1, 1930; H. H. SEMMES .AIHFOIL CONSTRUCTION Filed June 19, 1929gwventoz EMMES Patented Apr. '1, 1930 UNITED-STATES PATENT OFFICE HARRYH, SEMMES, or CHEVY CHASE, MARYLAND, nssrenon ro nnnmx nvm'rronoonronn'rron, on NEW YORK, N. Y.,-A con1 onA'rIoN or DELAWARE .unroinconsrnue'rroiv Application filed June 19,

The invention relates to airfoils and more particularly has reference toan airfoil which possesses great strength and rigidity.

In'the past there have been two general 5 designs'employed in .theconstruction of all I metal airfoils. One method makes use of aplurality of metal ribs shaped to conform to the camber of the wing andprovided with a plurality of openings to allow the spars to passtherethrough. The other design employs spars of girder form, eitherchannels or beams, generally of built up members, and bracing members orribs, in the form ofbridge truss chords and diagonals, placed betweenthe girders normal to their longitudinal axis. While the first mentionedconstruction has the advantage thatthe ribs support the surfacingmaterial, it possesses the defect that the spars do not; Moreover sincethe spars have a large cross sectional'area, a large opening must beprovided in the ribs to allow them to pass therethrough withvtheattendant result of a diminished rib resistance to any force applied tothe airfoil. 7 To bvercome this, the 5 rib must be given a greater depthwhich results in an increase in weight of the rib. Although inairfoils'employing a frame of girder like spars with ribs normal to thegirders and formed of crossed diagonals having top and bottomchordmembers, the surfacing material may be supported upon the ribs andgirders, and the whole may be formed into a continuous structure, theypossess the disadvantage that their fabrication is very costly. It iswell known that excluding the motor, the materials'used in'an airplanerepresent from 6% to 8% of its total cost. the principal expense beingthe labor. The difliculties of constructing such'an airfoil may be seento lie considerably in its multiplicity of parts, all of which must beaccurately formed with a minimum tolerance limit being allowed. The ribsmust be accurately cut to fit between the girders and must be secured tothem by special shaped fittings. Usu-ally the girders are of built upmembers of the I beam type although channels are sometimes used andthis-requires an additional amount of accurate workmanship.

Such construction also results in an in- 1929. Serial No. 872,156.

crease in the weight of the girder itself due to the additional materialrequired by the flanges .of the girder so that they may be connected tothe web. One of the requisites of an airfoil is that it must be light inweight. In

the foregoing design, because of the necessity of the chords, thecrossed diagonals and the securmg fittings for them, considerable weightis given to the airfoil which reduces the useful load that can becarried to meet a specific performance.

To overcome the ,difliculties mentioned above, designers have employed amodified construction.-comprisin "two girders and a plurality of ribsspaced between them. However, in such a design the surfacing material isformed in wide strips and these are laid over the frame work so thattheir ends overlap each other and may be connected together. Thisdesign, however,-presents only a small saving in the weight of theairfoil and it is nearly as difficult to fabricate.

I am aware that airfoils having an internal'corrugated member or membersequal in width thereto and running the full length of the airfoil havebeen emplpyed in place of the spar and rib types of construction. Insuch an airfoil, the surfacing material is supported upon thecorrugations. While airfoil's. of this type are of simple and continuousconstruction, they have the serious defect that,

because of the corrugated member being equal to their full length, theypossess. extreme weight. i

The major object of the invention is the design ofan airfoil which is acontinuous structure.

Another object of the invention is the con struction of an airfoilprovided with an internal continuous frame. i

Another object of the invention is the construction of an airfoilprovided with a'continuous internal frame for supporting the surfacingmaterial.

Another object of the invention is the con struction of an airfoilprovided with an internal continuous frame comprising a plu-. rality ofgirder like spars and wavular shaped ribs.

Another object of the invention is the conleading to the trailing edgeof the struction of a. rib for an airfoil of wavularlike shape so thatthe surfacing material may be supported upon the crests and troughs ofthe rib.

Yet another object of theinvention is the construction of a wavularshaped rib'of relatively small thickness and width.

Yet another object of. the invention isthe construction of an airfoilprovided with girder like spars having a plurality of open: ings thereinso as to allow the ribs to pass through the spars.

Still another object of the invention is the Construction of an airfoilprovided ,with an internal frame comprising a plurality of girder likespars and ribs adapted to pass through the spars and to extend from theairfoil.

Still another object of the invention is the construction. of an airfoilprovided with an internal continuous frame of girder like spars andwavular shaped ribs, the surfacing material being supported upon andfused to ort-ions of the ribs and to the spars for t ei'r full length. 1

Still another object of the invention'is to provide an airfoil which isof simple construction and of relatively low cost to fabri:

which may be incident to my improvements, the incate.

With these and other objects in view,

vention consists in the parts and combination to be hereinafter setforth and claimed, with the understanding that the several necessaryelements compris'lngmy invention may be varied in construction,proportions and arrangement without departin from the spirit and scopeof theappended c aims.

The present invention deals with airfoils, and consists in theconstructionof an airfoil which is a. continuous structure. One methodof practically eflecting the concept of this invention is to supportthesurf acin material upon an internal frame, comprisinga girder likespars and wavular adapted to pass through theplurality of shaped ribs,spars and to be secured thereto.

In order to make my invention more clearly understood, I have shown inthe accompanying drawings, means for carrying the same into practicaleffect without limit ing the improvements in their useful applicationsto the particular constructions which, for the purpose of explanation,have been made the subject of-illustration.

In the drawings:

Figure 1 represents atop View of the airfoil with a portion of thesurfacing material partially broken away.v

l igure 2 represents a cross section of the airfoil showing an outlineof one of the ribs is supported upon and connected to the ribs takenalong the line -2-2 of Figure 1.

Figure 3 is a pictorial representation showing a partial view of one ofthe wing'spars with the rib arrangement employed.

" each Referring to the drawings, like numerals represent like partsthroughout the several sired, girders having other sections, such as Ibeamsiand channels, may be employed without departing fromthe spirit ofthe invention. 7 The transverse axis of the airfoil and have their webspositioned parallel to the longitudinal axis thereof. g

Provided in'eachZ bar member 3 are a plurality of openings 5 adapted toallow the ribs 4 to pass'thereth rough. Openings 5 are positionedsubstantially along the longitudinal neutral axis of each girder memberand they are respectively spaced at equal distances. Lightening holes 6are provided in each spar 3 if desired.

Each rib4 has a wavular or curvilinear shaped outline, cc nprisingaseries of waves of varying lengths and amplitudes having crests 7 andstantially equidistant from any two girders. It should be noted that therib wave of greatest amplitude is formed upon the forward part of therib, that is, forward of the longitudinal center line of the airfoil.From Figure 2, it may be observed that theforward end 9 of each rib isbent backwardly towards the trailing edge of the airfoil, while theafter or rearward end of the rib is bent towards the leadingedge of theairfoil, and both-bent portionsof each rib are shaped to conform to theairfoil contour and are par- .allel thereto'for a substantial distance.

As shown in Figure 3 the wave outline of rib is of adjacent direction tothat of any preceding rib. Thus all points 'on the ribs incontact withthe surfacing material andlying in a line parallelto the longitudinalaxis of the airfoil are alternately on the top and bottom surfaces ofthe wing] Ribs 4 are adapted-to pass through the openings 5 and theportions thereof surrounded by the Z Ibar members are secured thereto.

In the construction shown the surfacing material is supported-upon theleading and trailing edges and the crests and troughs of the ribs andupon the flanges of the girder like members. Since the surfacingmaterial and spars it takes part of the load itself and thusadds furtherstrength to the airfoil. The girder members 3 provide transverse girders3 are spaced along the bracing thereto besides strength to. the girders.

By shaping the leading and trailing edges giving additional of each ribso that theyare'parallel to the arranging each rib so that its waveoutline isopposite in direction to that of any adjacent rib, it isevident that the beneficial effects of a staggered truss are obtained.Since the crests and troughs of the ribs are-arranged so as to supportthe surface material midway between any two I girders" they materiallyaid in taking care of stresses arising in the area between any twospars. Asis well known, the center of pressure in good airfoil design islocated forwardly of the longitudinal center line of the wing. Moreover,the greatest forces acting upon an airfoil oceur forwardly ofthis centerline. To meet this fa t, it may be observed that towards the leadingedge of the airfoil, the amplitude of each wave in the curvilinearoutline of the rib increases.

The embodiment of the invention allows the framework of the girders andribs to be tied together by reason ofthe ribs being secured to thegirders and the whole airfoil to be formed into a continuous-structureby reason of the surfacing material being supported upon and connectedto the leading and trailing edges and the crests and troughs of the ribsand the girder flanges. Should any particular member be stressed, aportion of its load is transmitted to every part of the airfoil and theother members carry a part of it. Hence every member has a strengtheningeffect upon the other members of the airfoil.

The airfoil is intended to be constructed of metal material, the ribsand girder members being of thin cross-section. while the snr or fused.\Vhen such metal is employed, the

skin of the airfoil is fused to the leading and trailing edges and thecrests and troughs of the ribs and to the flanges of the girders.Similarly, the ribs are secured to the webs of the girders where theypass through them.

.Should it be found desirable to use metal which is difficult to weld.such as aluminum or its alloys, the airfoil skin may besecured to theribs and girders by soldering, by the use of rivets, or by otherfastenings. In a similar manner theribs may be secured to the girders atpoints where they pass themthrough. V

In airfoil construction, it is desirable to have means accessible to theinterior of the airfoil so that the ribs and spars may be inspected.Should this feature be desired in connection with the invention, it isobvious that a portion of the upper surfacing material of the airfoilmay be formed of sheet metal and the remainder of fabric. 7

Although I have shown my invention as applied to an airfoil sectionhaving a Hat bot tom chord, I wish it to be distinctly understood that Ido not limit myself to this type of airfoil. Obviously the spirit of theinvention wouldinclude any kind of airfoil section, as for example adouble cainbered section, a section having its under surface entirelyconcave, or a combination ofa concave and a convex section.

The features of the airfoil construction will be appreciated from theforegoing descrip tion. It maybe seen that an airfoil which is acontinuous structure has. been formed. Moreover an airfoil, all themembers of which resist strain uponany particular member and allmembersof which act as bracing members for each other has been developed.Finally it may be seen that an airfoil which is of simple constructionand inexpensive fabrication has been designed.

\Vhile I-liave shown and described the preferred embodiment of myinvention, I wish it to be understood that I do not confine myself tothe precise details of construction herein set forth. by way ofillustration; as it is apparent that many changes and variations may bemade therein, by those skilled in the art,

without departing from the'spirit of the inveiition, or exceeding thescope of the append-- and surfacing material supported upon said ribs. I

2. Anairfoil comprising a plurality of cur- V'llillfifll shapedribshavinga wave-like outline the wave outline of each ribl'ieiiigkipposite in direct on to that'of any ad acent rib.

the leading and trailing 'ends of each .rib

shaped to conform 'to the contour of the airfoil, and surfacing materialadapted to be supported upon the leading and trailing ends and thecrests and troughs of said ribs;

3. An airfoil comprising'aplurality ofcurviliiiea-r shaped ribs having awave-like ontline the wave outline of each rib being opposite indirection to that ofany ad acent I'll)" and composed of a plurality ofwaves of 'vary- .w I I ing lengths and amplitudes. said waves; of

greatest amplitude occurring forwardlifiof "the longitudinal center lineof said airfoil and surfacing material adapted to be supported upon theribs. v

4. An airfoil comprising a plurality of internal Z bar members parallelto the longitudinal axis thereof. and said Z1-=bar members its beingoffa length substantially equal to that of the airfoil sheet surfacingmaterial supported upon the flanges of said Z.bars.

openings along their longitudinal axes of 5. An airfoil comprising aplurality of internal Z-bar members of a length substantially equal tothat of the airfoil positioned parallel to the leading edge thereof,said bars provided with a plurality of respectively equal spacedopenings along their longitudinal web axes, pass through said openingsand to be secured to the bar members and surfacing material adapted tobe supported upon the flangesof said Z bar members.

6. An airfoil comprising a plurality of girders, positioned parallelto'the longitudinal axis thereof, the girders being provided with aplurality of respectively equal spaced openings along their longitudinalWeb axes, a plurality of ribs having a curvilinear outline of wave-likeshape, the leading and trailing edges thereof being parallel to thecontour of the airfoil for a substantial distance and surfacing materialadapted to be supported upon the leading and trailing edges and thecrests and troughs of said ribs and upon the flanges of said girders.

7 An airfoil comprising a plurality of metal girders positioned parallelto the leading edge thereof, the girders being provided with a pluralityof respectively equal spacpld t e webs, a'plurality of metallic ribs ofcurvilinear outline having crests and troughs, the leading and trailingedges thereof being parallel to the contour of the airfoil for asubstantial distance, said ribs adapted to pass through the openlngs andto be fused to said girders and sheet metal surfacing material adaptedto be supported upon and fused -to the leading and trailing edges andthe crests and troughs of the ribs and the flanges of the girders. p

8. An airfoil comprising a plurality of girders positioned parallel tothe leading edge of the airfoil, the girders being provided with aplurality of respectively equal spaced openings along their longitudinalweb axes, a plurality of curvilinear shaped ribs having a wave-likeoutline, the wave outline of each rib being of opposite direction fromthat of any adjacent rib, said ribs adapted to pass through saidopenings and to be secured to each girder, and surfacing material,supportcd upon the ribs and the flanges of said girders. a I

9. An airfoil comprising a plurality of metal girders positionedparallel to the leading edge of the airfoil, the girders being providedwith a plurality of respectively equal spaced openings along theirlongitudinal web axes, a plurality of metallic curvilinear shaped ribshaving a wave-like shape, the wave outline of each rib being of oppositedirection from that of any adjacent, rib, said ribs adapted to passthrough said openings and to be fused to each girder and surfacing aplurality of ribs adapted to material adapted to be supported upon theshape the outline of each rib being opposite in direction to that of anyadjacent rib, the

leading and trailing edges of each ribbeing shaped to conform to thecontour of the'airfoil, said ribs adapted to pass through said openingsand to be secured to each girder and surfacing material adapted to besupported, upon the leading and trailing; edges and the crests andtroughs of each rib andupon each girder flange.

11. In an airfoil, a plurality of metal girders positioned parallel tothe leading edge thereof, the girders being provided with a pluralityofrespectively equal spaced open- ,4 along the longitudinal axes of their111%? we s, a plurality of metallic ribs of curvilinear outline, havinga wave-like shape, the outline of each rib, being of opposite directionto that of any adjacent rib, the leading and trailing edges thereofbeing shaped to conform to the contour of the airfoil, said ribs adaptedto pass through said openings and to be fused to the girders, and sheetmetal surfacing material adapted to be supported upon and fused to theleading and trailingedges and the crests and troughs of the ribs and theflanges of the girders.

12. An airfoil comprising a plurality of girders positioned parallel tothe-leading edge thereof, the girders being provided with a plurality ofrespectivelyequal spaced openings along their logitudinal web axes, aplurality of curvilinear shaped ribs, each rib outline comprising aseries of waves of varying lengths and amplitudes, the leading andtrailing edges thereof being shaped to co nform to the contour of theairfoil, said ribs adapted to pass through said openings and tobesecured to the girders, and surfacing material adapted to be supportedupon said ribs, and the flanges of said girders.

13. airfoil comprises a plurality of metal girders positioned parallelto the leading edge thereof, the girders being provided with a pluralityof respectively equal spaced openings along their longitudinal web axes,

and plurality of metal ribs of curvilinear positioned parallel to theleading edge thereof, the girdersbeing provided with a plurality 0respectively equal s aced openings along their longitudinal we axes, 9.P111: rahty of ribs having a curvilinear outline of wave-like shape, thewave outline of each rib bemg opposite in direction to that of any adacent rib and comprising a series of waves of varying lengths andamplitudes, said ribs adapted to pass through said openings and to besecured to each girder and surfacing material adapted to be supportedupon the ribs and the flanges of the girder.

15. In an airfoil a plurality of metal girders positioned parallel tothe leading edge thereof, the girders being provided with a plurality ofrespectively equal spaced openings along their longitudinal web axes, aplu-' rality of metallic ribs having a curvilinear outline of wave-likeshape, each rib having a wave outline opposite in direction to that ofany adjacent rib and comprising a series of waves of varying lengths andamplitudes said ribs adapted to pass through said openings and to befused thereto and sheet metal surfacing material adapted to be supportedupon and fused to the ribs and the girderfianges. r

- .16. A .one piece continuous rib for an airfoil,adapted to extendtransversely from the leading to the trailing edge of said airfoil,

' the forward end of said-rib being bent backwardly towards thetrailingedg'e of the airfoil in such a shape as to conform to theairfoil contour.

17. A one-piece continuous rib for; an airfoil adapted to extendtransversely from the leading edge to the trailing edge of said'airfoil, the forward end of said rib being bent backwardly towards thetrailing edge of the airfoil, the rearward. end -of said rib being bentforwardly towards the leading edge of the airfoil, both of said bendsbeing of such shape as-to conform to the airfoil contour. 18. Aone-piece continuous rib for an air foil, said rib having a curvilinearoutline 1 comprising crests and troughs, adapted to i support thesurfacing material of the airfoil,

the rib extending transversely of the airfoil from its leading to itstrailing edge, the forward end of said rib being bent backwardlytowardsthe trailing edge of the airfoil, the after end of said rib being bentforwardly towards the leading edge of the airfoil, saidbends being sosha ed as to conformito the contour of the air oil and adapted tosupport the surfacing material adjacent thereto. In testimony whereof Iafiix my signature.

' HARRY H. SEMLIES.

